Extension ladders are two ladders of equal height which are connected to each other and can extend to double their height, as one rises on tracks installed along the other. Install a pulley system on this ladder which will allow you to easily lower the longer section of the extension ladder without any trouble or without having to awkwardly lay the ladder down.
Attach the pulley to the second highest rang of the ladder and hook it onto the rang with a metal clasp or drill it into the rang with small metal screws. These pulleys can vary in size but they should be large enough to hold the rope you plan on using, which should be able to hold the weight of the ladder--if not more--without breaking. Make sure the rope runs smoothly through the pulley before installing.
Choose the Rope
Enough rope will be needed to run around the rang below the pulley, through the pulley and down the length of the ladder to the bottom or the second to last rang of the other ladder. It's probably a good idea to buy more rope than you need so you can cut it and tie it off without having to worry about running out of rope, so buy a length which is as long as the full extended ladder. Nylon mountaineering rope is most likely the strongest you can buy; it is also waterproof and will take much longer to fray and break apart.
Once you have selected your rope and attached your pulley, setting up the extension ladder rope is easy. Tie off the rope to the rang below the pulley in a tight knot. You can even secure this knot with a metal clasp so you can be sure it doesn't go anywhere or come undone when you are using it. Run the other end of the rope through the pulley, running all the way down to the second to last rang of the other ladder. Wrap it around that rang and pull it tight, so that the rope will maintain that tightness when the ladder is extended. Tie off the rope to the bottom rang and cut off the excess rope.